PWHT is used to do what?

PWHT is used to do what?

• A. Increase hardness only
• B. Relieve residual stresses
• C. Reduce weld size
• D. Improve machining

Answer: (B)

Post-weld heat treatment is used to relieve residual stresses created by welding. When metal cools after welding, the weld metal and heat-affected zone develop uneven contractions, leaving tensile stresses that can lead to cracking or distortion in service. Heating to a controlled temperature, holding for a specified time, and cooling slowly allows the metal’s atoms to rearrange and stresses to relax. This also can temper the microstructure and improve toughness and ductility. It doesn’t aim to increase hardness (in fact it often reduces it in many steels), nor does it reduce weld size or primarily improve machining. So PWHT’s main purpose is to relieve residual stresses.

Post-weld heat treatment is used to relieve residual stresses created by welding. When metal cools after welding, the weld metal and heat-affected zone develop uneven contractions, leaving tensile stresses that can lead to cracking or distortion in service. Heating to a controlled temperature, holding for a specified time, and cooling slowly allows the metal’s atoms to rearrange and stresses to relax. This also can temper the microstructure and improve toughness and ductility. It doesn’t aim to increase hardness (in fact it often reduces it in many steels), nor does it reduce weld size or primarily improve machining. So PWHT’s main purpose is to relieve residual stresses.